Various types of apparatus have been proposed for maintaining alertness of drivers and operators of machinery. U.S. Pat. Nos. 2,724,109 and 3,863,262 to Skolnick et al describe a sleep inhibitor for automobile drivers wherein light from a lamp is reflected from the driver's eyeball in order to activate an alarm when the eyeball is covered by the eyelid for more than a predetermined time. U.S. Pat. No. 3,379,885 to Nork describes a sight switch employing an infrared source and sensor which distinguishes between reflections from the white of the eyeball and the iris. Two other U.S. Pat. Nos. 4,397,531 and 4,625,337, use relatively expensive two dimensional image scanners and very heavy software to analyze the image.